1. Statement of the Technical Field
The invention concerns clamping mechanisms, and more particularly, clamping mechanisms for fastening printed circuit boards or printed circuit cards to chassis.
2. Description of the Related Art
Traditionally, circuit card clamps have been used for fastening circuit cards within a slot of a chassis such as a heat exchanger, heat sink, or cold plate. For example, U.S. Pat. No. 4,775,260 to Kecmer and U.S. Pat. No. 5,071,013 to Peterson describe circuit card clamps consisting of a threaded rod with wedge-shaped bodies disposed thereon. A circuit card clamp coupled to a circuit card can be inserted into a chassis slot. Subsequently, the threaded rod can be rotated with a tool (i.e., torque wrench) in order to shorten the length of the circuit card clamp. By shortening the circuit card clamp, the wedge-shaped bodies are compressed thereby creating an increase in the circuit card clamp's width. As a result, a clamping force is exerted by the circuit card clamp securing the circuit card to the chassis.
The above described circuit card clamps suffer from certain drawbacks. For example, the threaded rod needs to be turned to create a desired clamping force by the circuit card clamp. The threaded rod also needs to be turned to create a clamping force which ensures contact between a circuit card and a heat sink, thereby providing efficient thermal conductivity. Often, specific clamping forces are required to prevent loosening of circuit card from chassis due to external forces (e.g., vibration forces). Of necessity, torque wrench measurements have been required to prevent over tightening of the threaded rod which can damage the circuit card and may strip the threaded rod. This process requires using external tools. Ultimately, the clamping device and the thermal performance of the circuit card clamp's architecture are limited by the size of the threaded rod. For example, the size of the threaded rod dictates the quantity of wedge-shaped bodies included in a circuit card clamp assembly.
U.S. Pat. No. 5,224,016 to Weisman et al. describes a circuit card clamp having a rail with wedge-shaped bodies disposed thereon. Such a circuit card clamp assembly is similar to the wedge architectures described above. However, this circuit card clamp assembly provides a tool-free insertion and extraction of the circuit card from the chassis.
This circuit card clamp assembly similarly suffers from drawbacks. For example, the clamping device is limited by the quantities and the strength of the beveled washers which create the clamping force. This limitation typically results in an insufficient clamping force exerted by the circuit card clamp for adequately fastening a circuit card to a chassis to prevent loosening of a circuit card.
Despite the various circuit card clamp assemblies known in the art there remains a need for a wedge assembly that is able to provide improved thermal performance by optimizing a thermal interface between a circuit card and a chassis. Also needed is a tool-free circuit card clamp assembly which provides improved clamping force for adequately fastening a circuit card to a chassis.